The present invention relates generally to semiconductor production. More precisely the invention relates to improved protection of semiconductor die bonds.
To facilitate discussion FIG. 1 is a front side view of a bump device 100 such as a flip chip, used in the prior art. The bump device 100 may comprise a die 102, with a plurality of solder bumps 108 mounted thereon. FIG. 2 is a cross sectional view of the bump device 100 mounted on a substrate 103. The die 102 may have a plurality of aluminum bond pads 104. A passivation layer 105 may be patterned around the aluminum bond pads. An under bump metal (UBM), such as a nickel, copper, etc. may be patterned on the aluminum bond pads 104 to improve bump reliability. Solder bumps 108 may be formed on the UMB and reflowed to mechanically and electrically connect the die 102 to the substrate 103. Thermal stress created by different coefficients of expansion between the die, substrate, and solder bumps may create cracks in the solder bumps near the UMB. In the prior art, after the die 102 is mounted to the substrate 103 an underfill material may be applied between the die 102 and substrate 103 and around the solder bumps 108 to reduce cracks created by thermal stress. Such underfill techniques may require the placement of underfill with each individual die 102 mounted on a substrate 103. Providing underfill individually to each individual die 102 may be expensive and time consuming, and may require accuracy in dispensing the underfill. The substrate 103 may be mounted to a circuit board 107 using a ball grid array. In such ball grid array (BGA) mounts, a solder mask 110 may be placed on a side of the substrate 103 and patterned to expose bond pads 112. A pad coating 114 may be placed over the bond pads 112. Solder bumps 116 may be connected to the pad coating 114. The solder mask 110 may be an organic material, which may be patterned using photo resist. The solder mask 110 may include liquid photo imagable materials. Solder masks are described in U.S. Pat. No. 4,666,821, entitled xe2x80x9cPhotopolymer For Use As A Solder Maskxe2x80x9d, by Hein et al. incorporated by reference. In the prior art, such solder masks may be applied to a substrate upon which a die is mounted as described in U.S. Pat. No. 5,796,586, by Lee et al. incorporated by reference or on circuit boards to protect the solder lines. Such solder masks may also be applied to circuit boards to protect solder wiring. For direct chip attach, the bump device is mounted directly to a PC board, so that the PC board is the substrate.
It is desirable to provide protection from thermal stress between a die and a substrate that is less expensive and easier and faster to apply.
To achieve the foregoing and other objects and in accordance with the purpose of the present invention, a variety of techniques for providing a protective layer for providing an improved flip-chip are described. Generally, chips are created as part of a wafer, wherein each chip has bond pads on a front side of the wafer. A patterned mask layer is patterned over the front side of the wafer, so that the patterned mask layer provides apertures over the bond pads. Electrically conductive connectors are formed on each of the bond pads, so that the patterned mask layer is in contact with at least a quarter of the electrically conductive connector. The chips are then singulated.
These and other features of the present invention will be described in more detail below in the detailed description of the invention and in conjunction with the following figures.